/**
* Data structure for a priority queue, array data structure in which each element additionally has a "priority" associated with it.
* In a priority queue, an element with high priority is served before an element with low priority
* @see https://en.wikipedia.org/wiki/Binary_heap
*/
class BinaryHeap {
constructor(scoreFunction = null) {
this.content = [];
this.scoreFunction = scoreFunction;
}
push(element) {
// Add the new element to the end of the array.
this.content.push(element);
// Allow it to sink down.
this.sinkDown(this.content.length - 1);
}
pop() {
// Store the first element so we can return it later.
var result = this.content[0];
// Get the element at the end of the array.
var end = this.content.pop();
// If there are any elements left, put the end element at the
// start, and let it bubble up.
if (this.content.length > 0) {
this.content[0] = end;
this.bubbleUp(0);
}
return result;
}
remove(node) {
var i = this.content.indexOf(node);
// When it is found, the process seen in 'pop' is repeated
// to fill up the hole.
var end = this.content.pop();
if (i !== this.content.length - 1) {
this.content[i] = end;
if (this.scoreFunction(end) < this.scoreFunction(node)) {
this.sinkDown(i);
} else {
this.bubbleUp(i);
}
}
}
size() {
return this.content.length;
}
rescoreElement(node) {
this.sinkDown(this.content.indexOf(node));
}
sinkDown(n) {
// Fetch the element that has to be sunk.
var element = this.content[n];
// When at 0, an element can not sink any further.
while (n > 0) {
// Compute the parent element's index, and fetch it.
var parentN = ((n + 1) >> 1) - 1;
var parent = this.content[parentN];
// Swap the elements if the parent is greater.
if (this.scoreFunction(element) < this.scoreFunction(parent)) {
this.content[parentN] = element;
this.content[n] = parent;
// Update 'n' to continue at the new position.
n = parentN;
}
// Found a parent that is less, no need to sink any further.
else {
break;
}
}
}
bubbleUp(n) {
// Look up the target element and its score.
var length = this.content.length;
var element = this.content[n];
var elemScore = this.scoreFunction(element);
while (true) {
// Compute the indices of the child elements.
var child2N = (n + 1) << 1;
var child1N = child2N - 1;
// This is used to store the new position of the element, if any.
var swap = null;
var child1Score;
// If the first child exists (is inside the array)...
if (child1N < length) {
// Look it up and compute its score.
var child1 = this.content[child1N];
child1Score = this.scoreFunction(child1);
// If the score is less than our element's, we need to swap.
if (child1Score < elemScore) {
swap = child1N;
}
}
// Do the same checks for the other child.
if (child2N < length) {
var child2 = this.content[child2N];
var child2Score = this.scoreFunction(child2);
if (child2Score < (swap === null ? elemScore : child1Score)) {
swap = child2N;
}
}
// If the element needs to be moved, swap it, and continue.
if (swap !== null) {
this.content[n] = this.content[swap];
this.content[swap] = element;
n = swap;
}
// Otherwise, we are done.
else {
break;
}
}
}
}
export default BinaryHeap;